Whenever the Prophet ﷺ performed the bowing, he kept his back level, neither lowering his head nor raising it, and placed his hands upon his knees.
أخبرنا محمد بن بشار قال حدثنا يحيى قال حدثنا عبد الحميد بن جعفر قال حدثني محمد بن عمرو بن عطاء
كان النبي ﷺ إذا ركع اعتدل فلم ينصب رأسه ولم يقنعه ووضع يديه على ركبتيه
Bukhari narrated it in Adhan, in the chapter on the practice of sitting during the testimony of faith, no. 828, from the hadith of Muhammad bin Amr bin Ala, transmitted through him at length, and it is also found in Kubra, no. 627.Tirmidhi also narrated it, no. 304, from Muhammad Ibn Bashar and others, at length, and said, "hasan sahih."Ibn Khuzayma, Ibn Hibban, Bukhari, and others graded it sahih.